Not Applicable
Not Applicable
1. Field of the Invention
The invention relates to radio frequency identification (RFID) reader power output, and more particularly a method of pulsed and continuous power output for an RFID reader.
2. Description of the Related Art
RFID systems are increasingly used for a variety of applications including inventory control and article monitoring. In RFID systems, an RFID reader transmits an RFID interrogation signal. An RFID marker or tag receives the transmitted RF interrogation signal and responds with a reply signal that includes identification information and other data as known in the art. The RFID reader receives the RFID marker""s reply signal and recovers the relevant information contained within the signal. The RFID marker must be within a predetermined maximum radius from the RFID reader for the RFID reader to be able to detect and retrieve data from the RFID marker""s reply signal. If the RFID reader does not receive a reply signal, the RFID reader will continue to transmit the RFID interrogation signal, which will be radiated into the environment.
Passive RFID tags are powered by the transmitted interrogation signal from the RFID reader. When the interrogation signal is received, the tag will reply with its stored data. The time for round trip communication between the reader and marker is dependent on the amount of data being transferred and the data rate. When there are multiple tags within the transmitted interrogation signal, a multi-tag algorithm is used to sort out the data from each tag, which increases the read time. Finding a single tag may take on the order of 10 msec, and up to 100 msec or more if there are a larger number of tags in the area. The slowing of read time is related to how the system handles the previously read tags. Once a tag has identified itself to the reader and its data is transferred, the tag is instructed to xe2x80x9crememberxe2x80x9d that it was read and stops replying to the interrogation field. The reader can then go onto the next tag. When the interrogation field incident on a tag drops below a threshold value, the tag times-out, or xe2x80x9cforgetsxe2x80x9d that it was read. The tag will be reset and begin to respond again when the interrogation field rises above the threshold value. Tags located at the fringe of the interrogation field level corresponding to the threshold value for powering a tag will be constantly resetting. If tags try to re-communicate at frequent intervals, the multi-tag algorithm will slow and may not be able to read all the tags within the reading range.
The speed and range of reading is reduced according to the number of tags being powered by the interrogation signal and the power level of the field. To improve the situation active RFID tags can be utilized. An active RFID tag includes a battery to power the tag. Unfortunately, active RFID tags are too expensive for many applications. Alternately, RFID readers can transmit at higher power levels to keep multiple passive tags powered during reading, providing for increased read range. However, restrictions on RF emissions limit the power level at which RFID readers can operate.
The present invention provides a method to power an RFID reader to increase multi-tag-reading capability, and increase passive reading range without maximizing the transmitted power level. The method encompasses transmitting a radio frequency identification interrogation signal to increase a radio frequency identification tag reading range by first transmitting a pulsed radio frequency identification interrogation signal. When a response signal from a radio frequency identification tag is received, the pulsed radio frequency identification interrogation signal and a continuous radio frequency identification interrogation signal are transmitted simultaneously. After no further response signals from radio frequency identification tags are received, the system again begins transmitting only the pulsed radio frequency identification interrogation signal.
The method further includes, after receiving a response signal, reading data associated with the radio frequency identification tag, and, then turning the radio frequency identification tag off so that it no longer responds to the radio frequency identification interrogation signal.
The method may also include, prior to transmitting only the pulsed radio frequency identification interrogation signal after not receiving a response signal from another radio frequency identification tag, turning all radio frequency identification tags on. Alternately, only a specific or preselected radio frequency identification tag is turned on.
Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention.